A synthesis method for linear methylchloropolysiloxanes has already been reported by Winton Patnode and Donald F. Wilcock in J. Am. Chem. Soc., volume 68, page 358 (1946).
In the above-cited method, a mixture of purified water and dioxane is introduced into dimethyldichlorosilane dissolved in a large quantity of diethyl ether. However, using a large quantity of diethyl ether is dangerous in handling and impairs the production efficiency per unit volume. Therefore, that method has a defect of having no suitability for production on an industrial scale.
In addition, the foregoing report describes experimental results such that a mixture of linear methylchloropolysiloxanes with cyclic dimethylpolysiloxanes is produced when purified water by itself is introduced into dimethyldichlorosilane alone, the linear product and the cyclic product thus obtained are hard to separate because their boiling points are very close to each other, and the linear methylchloropolysiloxanes, which are more useful than the cyclic product, are produced therein in low yields.
In order to solve the above-described problems, therefore, we have made intensive studies. As a result, it has been found out that in hydrolyzing dimethyldichlorosilane by introducing thereinto a water solution containing a water-soluble oxygen-containing organic compound, linear dimethylpolysiloxanes alone, having both ends blocked with chlorine atoms, can be selectively produced when the water solution introduced is rendered acidic and the quantity of water introduced into the hydrolysis system is controlled properly; while cyclic dimethylpolysiloxanes alone can be selectively produced by properly controlling the quantity of water introduced into the hydrolysis system and, if desired, the water solution is rendered acidic; thereby achieving the present invention.